The Sleeper, Welsh National Youth Opera, Cardiff

“These premises have 24-hour security surveillance,” reads one of the notices on the wall as we audience traipsed round the outside of Cardiff’s Coal Exchange between stages of this mobile production of Stephen Deazley’s new opera about people who can’t sleep. It turned out to be the only poster that had nothing to do with the performance, in among the “Nobody Sleeps” signs, the “Keep Awake”s, the “No Beds” (or whatever: “Nessun dorma” I didn’t see or hear, but might have done; it would have been thematic and does in fact crop up in the libretto).

Personally, I’m one of (I hope) billions for whom “promenade” performances of this kind are a waking nightmare. I dread being instructed which door I have to go through, when, by a woman in a black T-shirt with a walkie-talkie. I dislike being fingered through side entrances by pale girls in woolly hats. I loathe standing in dark, smoke-filled foyers feeling supernumerary while those same pale girls and boys rush around with haunted looks and meaning gestures to the sound of an electronic tape.

I am, in short, irritated by this blithe assumption that, having bought (or in this case, I’m happy to say, been given) a ticket in all innocence for a Friday-night show, I am fair game for manoeuvring, manipulating, manhandling, without fee, rather than being left to subside and, if I so wish, fall asleep (yes) in a bucket seat with inadequate leg room.

Above all, I get cross when I realise that all this palaver is totally irrelevant to what I’m seeing and hearing, a mere gimmick, an aren’t-we-up-to-the-minute-politically-switched-on-and-theatrically-à-la-page add-on to the business of entertaining, stimulating, illuminating and even, if you like, challenging us with strong, coherent ideas, vigorous staging and, above all, first-rate music.

All of which, I have now to admit, are on offer in this production by Welsh National Youth Opera, a deeply serious, professional-minded and well-run subsidiary of WNO which puts on shows largely or entirely cast, played and staged by under-25s. The Sleeper was written for them and fits them like a glove.

I read Michael Symmons Roberts’s libretto, and still have very little idea what it’s all about (the words are largely indecipherable in performance). But then what’s new about opera you can’t understand? Surtitles have, of course, ruined incomprehension. But the Coal Exchange and promenade performance will surely reinstate it.

Roughly speaking, though, we are in a world without sleep: hence the pale girls and the haunted looks. They all live in a Nibelheim-like squat, working 24/7, and, not surprisingly, getting on one another’s nerves. Along comes a girl who can sleep, and who naturally enough becomes an object of curiosity, study and, eventually, mildly pornographic investigation, photography and molestation.

But long before this I lost the thread. In the final scene there is a cage with a bed in it, and a man called Hypnos (naturally) whose mother – I think – could sleep, and who (consequently?) is a little too interested in sleeping girls. No doubt sleep here is a metaphor for – well, for something. But not for power, surely, because in this particular country of the blind, the one-eyed girl is emphatically not queen. She is victim, unless of course she sleeps with the one eye open.

Obscure it may be, but this is a work that positively exudes talent. Deazley’s music, much of it choral, but with some strong solo writing and a brilliantly telling instrumental accompaniment (five strings, flute, clarinet and percussion), is compelling throughout, lively in rhythm and colouring, superbly well paced. The pitch of the style, I suppose, is vaguely post-Menotti, with the same instinctive mastery of stage movement, but better, more refined, less facile. I enjoyed every minute of it.

In particular, Deazley writes marvellously well for chorus, and the WNYO repay him with choral singing of a precision and intensity I could listen to for hours. The solo singing is also excellent, especially by Emily Griffiths as the sleeper, Tim Nelson as the kinky Hypnos and Celine Forrest as his daughter Somnus (Nelson and Forrest pictured left), and the whole thing is conducted con bravura by Tim Murray.

As for Pete Harris’s staging and the designs of Rhys Jarman and Rachael McCutcheon, they clarify little in the narrative sense, but are nonetheless compulsively watchable. How is this possible? Because, I think, good theatre is as much to do with movement and image as with storytelling, and Harris has these young singing actors singing and acting as if their lives depended on it. The pale girls and boys turn out to be red-blooded performers. And as for falling asleep, don’t even think about it.